"
"By heating the steam, the vapor may acquire a volume forty thousand
times greater than that of the water; all that is well known; but as
soon as it comes in contact with the air, nothing is left of it but a
cloud, which collapses again into a few drops of water."
"That may be all very true, Master Fritz, if the steam were allowed to
escape into the air; but it is only permitted to do that after it has
done duty on board ship. It appears that steam is very elastic, and
may be compressed like India-rubber, but has a tendency to resist the
pressure and set itself free. Imagine, for example, a headstrong young
man, for a long time kept in restraint by parental control, suddenly
let loose, and allowed scope to follow the bent of his own
inclinations."
"Very good, Willis; for argument's sake, let us take your headstrong
young man, or rather the steam, for granted, and let us admit that it
is as elastic as ever you please--but what then?"
"Then you must imagine a piston in a cylinder, forced upwards when
the steam is heated, and falling downwards when the steam is cooled.
Next fancy this upward and downward motion regulated by a number of
wheels and cranks that turn two wheels on each side of the ship,
keeping up a constant jangling and clanking, the wheels or paddles
splashing in the water, and then you may form a slight idea of the
thing.
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